1cat2ferrets Posted February 8, 2010 Share Posted February 8, 2010 ok, here goes.. a person has a mass of 50kg sits on a lever and lifts a mass of 100kg a distance of 5m. what is the mechanical advantage of the lever? a. 1 b. 1 1/2 c. 2 d. 50 or e. 100? my guess is d. 50 because M=f*d. the largest dinosaur was the brachiosaurus, which had a mass of 77,000kg. what was the weight of the dino in newtons? i know that 1kg=9.8N so, 77,000kg * 9.8N=754600N, right? second part of question: if the dino had lived on a planet whose gravity was half that of earth's what would have been its mass? what would its weight in newtons have been? ok, I know that mass doesn't change no matter where it is, so the answer is 77,000kg, right? I don't know how to get the weight, or would it be the same also?? TIA! Quote Link to comment Share on other sites More sharing options...
JillZ Posted February 8, 2010 Share Posted February 8, 2010 For the weight/mass question: Think of the weight as the force exerted downwards by an object due to gravity. weight = force = mass x acceleration. On Earth, the acceleration due to gravity is 9.8 m/s^2. That means a 1 kg mass would weigh: weight = mass x acceleration = 1 kg x 9.8 m/s^2 = 9.8 kg*m/s^2 = 9.8 N So if gravity was, say, half of Earth's gravity, then the acceleration due to gravity would be 9.8 m/s^2 / 2 = 4.9 m/s^2. The mass stays the same (as you stated), but the new weight is now weight = mass x acceleration = 1 kg x 4.9 m/s^2 = 4.9 N So if the gravity is half of Earth's, the weight is half of what it is on Earth. For the dinosaur, just substitute in the correct mass and you will have the weight. Hope this helps! Quote Link to comment Share on other sites More sharing options...
mpcTutor Posted February 8, 2010 Share Posted February 8, 2010 The other poster is right. Part I ------- Mechanical advantage by definition is Load/Effort, hence MA = 100g/50g = 2 Part II -------- If you wrote 77,000kg * 9.8N=754600N, there will be sufficient reason to lose points. Correct answer would be (77, 000 kg) (9.8 m/s^2) = 754, 600 N Part III -------- As you pointed out mass would remain unchanged, thus mass = 77, 000 kg Weight is force which is directly proportional to g for a given mass m, hence weight would be (1/2)(754, 600) N = 377, 300 N Best regards. MPCTutor --------------------------------------------------------------------------- AP Calculus, AP Physics, Singapore Math Grades 7-12 --------------------------------------------------------------------------- US Central Time: 4:38 PM 2/8/2010 Quote Link to comment Share on other sites More sharing options...
AngieW in Texas Posted February 8, 2010 Share Posted February 8, 2010 I agree with the other posters. Quote Link to comment Share on other sites More sharing options...
1cat2ferrets Posted February 9, 2010 Author Share Posted February 9, 2010 for the help. At least, my son and I are almost figuring this stuff out! LOL Quote Link to comment Share on other sites More sharing options...
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